A white light-emitting LED device, which is a single device comprising a phosphor and a semi-conductor light-emitting element such as LED in combination so as to give off white light, is becoming popularly used nowadays as a light source for illumination and the like. The phosphor employed in the white light-emitting LED device is required to exhibit high luminous efficiency when excited by near UV to blue light. For use as that phosphor, various oxynitride phosphors have been proposed.
For example, many europium-activated SiAlON phosphors are disclosed as the above phosphors. They are, for example, regulated by the compositions in particular ranges and/or by the positions of X-ray diffraction lines. In addition, production methods thereof and raw materials for their production are also variously disclosed.
The raw materials for producing SiAlON phosphors generally include nitrides, oxides, hydroxides and carbonates of metals, such as, strontium, europium and silicon, which constitute parts of the phosphors. However, characteristics of the resultant phosphor are often dependent on what kind of metal compound is adopted. For example, if produced according to a known method in which strontium is supplied in the form of carbonate, the resultant SiAlON phosphor contains a variant phase emitting blue luminescence. On the other hand, if the raw material of strontium is in the form of nitride such as Sr3N2, formation of the variant phase can be avoided. However, strontium nitride materials are so chemically unstable and expensive that they are difficult to use industrially.
The present inventors are now independently studying and developing a method by which europium-activated SiAlON phosphors less containing variant phases can be produced from strontium oxide or hydroxide in place of unstable and expensive Sr3N2 through intermediate products formed by plural steps. However, a red light-emitting SiAlON phosphor produced by that method is still required to give off luminescence at a longer wavelength and hence has room for improvement.